Graphics Reference
In-Depth Information
In this case, the
-d
denotes a decompression, the input file is a texture that has
already been compressed, and the output file is one of the uncompressed formats.
To see what a texture would look like compressed with a given set of options,
use the command
astcenc
−
t
<
input
.
file
><
output
.
file
><
rate
>
[
options
]
The
-t
option compresses the file with the given options then immediately de-
compresses it into the output file. The interim compressed image is not saved,
and the input and output files are both in a decompressed file format.
The options can be left blank, but to get a good result, there are a few useful
ones to remember.
The most useful arguments are the quality presets:
−
veryfast
−
fast
−
medium
−
thorough
−
exhaustive
Many options are available to set various compression quality factors, including
•
the number and scope of block partition patterns to attempt,
•
the various signal-to-noise cutoff levels to early out of the individual decision-
making stages,
•
the maximum iterations of different bounding color tests.
Most users won't explore all of these to find the best mix for their own needs.
Therefore, the quality presets can be used to give a high-level hint to the com-
pressor, from which individual quality factors are derived.
It should be noted that
veryfast
, although almost instantaneous, gives good
results only for a small subset of input images. Conversely, the
exhaustive
quality
level (which does exactly what it says and attempts every possible bounding
pattern combination for every block) takes a very much longer time, but it will
often have very little visible difference to a file compressed in
thorough
mode.
6.5 Using ASTC Textures
ASTC capability is a new hardware feature available starting in late 2013. To
get started with ASTC right away, the ARM Mali OpenGL ES 3.0 Emulator
[Mali 14b] is available from ARM's website, and this is compatible with ASTC
